The placenta provides the physiological interface between mother and fetus and is critically involved in controlling the environment in which the embryo/fetus develops. Trophoblast cells, the parenchymal cells of the placenta, differentiate along a multilineage pathway, and form the backbone of the gestational conduit that is essential for viviparity. These important cells produce hormones and cytokines that redirect the activities of the maternal environment and they possess transport machinery that facilitates the delivery of nutrients to the fetus. Disruptions in trophoblast development can lead to early pregnancy loss, intrauterine growth retardation, and tumorigenesis. These represent serious health problems whose etiologies are not sufficiently understood. The objectives of this project are to understand control mechanisms involved in regulating trophoblast cell differentiation. We focus on the role of the phosphatidylinositol 3-kinase (PI3-K)/akt pathway in the regulation of trophoblast cell differentiation. We propose that an essential feature of the differentiation of trophoblast giant cells is their acquisition of a constitutively activated PI3-K/akt pathway. The proposed research addresses three specific aims. Experiments outlined in Specific Aim No. 1 investigate the control of PI3-K/akt pathway activation during trophoblast cell development. Specific Aim No. 2 examines the impact of the PI3-K/akt pathway on the trophoblast cell phenotype, including endoreduplication, invasiveness, and endocrine function. Specific Aim No. 3 focuses on the identification of downstream targets of the PI3-K/akt pathway in differentiating trophoblast cells. The proposed studies utilize in vitro investigations with rodent trophoblast cell culture systems and in vivo analysis of rodent trophoblast cells developing in situ. Identification of regulatory mechanisms controlling trophoblast cell differentiation will provide a better understanding of placental development and insights into the etiology of early pregnancy loss, intrauterine growth retardation, and various disorders and neoplasms of the placenta.